The present invention relates generally to an input voltage sensing circuit for example for use with boost power factor correction in isolated power supplies and corresponding systems and methods.
Providing input voltage sensing for use with isolated power supplies is difficult. There are at least three types of circuits which have been attempted, including: (i) an attenuation network, (ii) a transformer connected to a power mains or rectified mains, and (iii) a flyback topology.
An attenuation network (e.g., a voltage divider) may be connected to a power input mains (e.g., an alternating current (AC) mains) or a rectified power input mains. Disadvantages associated with using an attenuation network include the inability for an attenuated signal to be available at an isolated secondary side and the attenuation network consuming a significant quantity of power, thereby decreasing overall system efficiency.
Numerous disadvantages exist for systems having a transformer connected to a power input or rectified mains. For example, to operate at typical power input mains frequencies such as 50 or 60 Hz, the magnetizing inductance of the transformer's primary winding must be high to avoid saturation. A high magnetizing inductance requires a large magnetic device, thereby increasing cost and requiring a significant amount of printed circuit board (PCB) space.
Sense circuits have been used to detect input voltage sensing in a line powered network (for example, as in U.S. Pat. No. 6,967,585 to Lomax, Jr. et al.). However, these sense circuits are described as using a flyback topology, and an indirect input voltage measurement must be sensed during a particular interval of a switching cycle (see, e.g., FIGS. 1 and 4 of Lomax, Jr.). As such, ease of use and applicability of a flyback topology is limited and is not robust.